Conventionally, electrical junction boxes to be mounted in automobiles and the like are configured to include a box body that has a peripheral wall formed in a frame shape and keeps electric parts such as a relay, a fuse, and an electric wire installed inside the peripheral wall, and lid bodies such as an upper cover and a lower cover with which opening portions on the upper and lower sides of the box body are covered. For example, electrical junction boxes are configured as disclosed in JP 2013-34320A (Patent Document 1).
In Patent Document 1, double wall portions, in which an inner wall and an outer wall extending in a peripheral direction are arranged with a clearance therebetween, are provided at the upper end portion of the peripheral wall of the box body and the lower opening end portion of the upper cover. The outer wall in the double wall portion of the box body is inserted between the inner wall and the outer wall in the double wall portion of the upper cover, and thus the upper opening portion of the box body is covered with the upper cover. Accordingly, even when the electrical junction box mounted in a vehicle is splashed with water, a route through which the water infiltrates from the outside into the inside of the electrical junction box becomes complicated due to the double wall portions of the upper cover and the box body overlapping each other, and therefore, the water is advantageously prevented from infiltrating into the inside of the electrical junction box through the portion where the upper cover and the box body are fitted to each other.
In addition, in the electrical junction boxes having such a conventional structure, as clearly shown in FIGS. 5 and 6 in Patent Document 1, a structure is widely used in which the upper cover is attached to the box body by engaging an engaging portion provided to one end of the upper cover with an engaged portion provided on one end of the box body and rotating the upper cover with the engaging portion serving as the rotation center. Accordingly, when attaching the upper cover to the box body, it is not necessary to precisely position the double wall portions of the upper cover and the box body over the entire length in the peripheral direction. Therefore, the upper cover can be easily attached to the box body, resulting in a shortening of the operation time and a reduction in manufacturing cost. In particular, in order to prevent the inner wall at one end of the upper cover from interfering with the outer wall of the box body during the rotation of the upper cover, an idea has been introduced in which the inner wall of the upper cover is formed such that a clearance is formed between the one end thereof and the outer wall of the box body.
However, the clearance between the engaging portion of the upper cover and the engaged portion of the box body, and the tolerance of the dimensions of the upper cover and the box body vary widely, and therefore, it is necessary to ensure a sufficiently large clearance between the one end of the inner wall of the upper cover and the outer wall of the box body in order to prevent the interference between the inner wall of the upper cover and the outer wall of the box body. With such a conventional structure, the size of the electrical junction box is inevitably increased, and there are cases where recent demand for the reduction in size of the electrical junction box cannot be met.